The effects of cooling rate on microstructure and room temperature tensile properties of equiaxed nickel-based cast superalloy K4750 were studied by designing shell insulation methods. Four types of insulation methods were designed, including sand-filled method, test bars without insulation felt, wrapped single-layer insulation felt and wrapped double-layer insulation felt, and the order of cooling rate at the test bars of the shell is test bars without insulation felt ≥ sand-filled method > wrapped single-layer insulation felt ≥ wrapped double-layer insulation felt. After standard heat treatment, the test bar with sand-filled shell has the highest room temperature tensile strength (1115 MPa), the test bar without insulation felt has the second highest strength (1095 MPa), and the single-layer insulation felt and the double-layer insulation felt have the worst strengths of 950 and 952.5 MPa, respectively. The microstructures of the alloy were characterized by OM, SEM and EBSD. The results show that the grains of sand-filled method, test bars without insulation felt, single-layer insulation felt and double-layer insulation felt are equiaxed crystals, and the average grain sizes are 176, 167, 325 and 315 μm, respectively. The cooling rate of the sand-filled and test bars without insulation felt alloys is faster, the formation of small equiaxed crystals can more easily coordinate deformation in the stress conditions, and the precipitated MC-type primary carbide is finer and mainly in the form of blocks, which is conducive to inhibit the expansion of microvoids and cracks during deformation, significantly improving the tensile properties of the alloy at room temperature. On the contrary, the cooling rate of the alloys prepared by single-layer insulation felt and double-layer insulation felt is slower, the formed large-size equiaxed crystals are not conducive to the coordinated deformation between the grains, and the precipitation of MC-type primary carbide with large size and long strip shape promotes the emergence and expansion of holes and microcracks, which significantly reduces the strength and plasticity of the alloy at room temperature. © 2024 Science Press. All rights reserved.
